X-Ray Microanalysis of Art Glass Surfaces
R.B. Simmons Briarwillow LLC, Atlanta, GA 30345
microscopy@briarwillow.com
Introduction In recent years there has been a virtual explosion in the
world of art glass. New glass formulations have brought a host of new colors into the marketplace, and the availability of low-cost, high-quality torches and other tools has brought art glass to the hobbyist. In addition to burn risks and possible cutting injury, there are a number of less obvious hazards that should be known to novice glass workers. One of these is the presence of heavy metals in or on glass surfaces and possibly in the atmosphere immediately surrounding the work area, presenting both potential skin contact and inhalation hazards. Tis study examines the metallic surfaces generated on five glass colors commonly used in art glass jewelry. Many of the colorants in glass are metallic compounds
(oxides, chlorides, etc.). Lead oxide is perhaps the best known glass additive and has been used in “lead crystal” for hundreds of years. It was first used on an industrial scale for crystal production by George Ravenscroſt in the mid-seventeenth century [1] and is a mainstay in the fine glassware industry. It does not impart color on its own but rather changes the refractive index and dispersion of the glass, giving cut and polished “leaded” glass its characteristic colorful flash. With the possible exception of long-term storage of acidic foods or liquids, this type of glass is safe for use with foods and for skin contact, presenting no health risk from lead exposure. Minute amounts of gold chloride impart a pink-red color to glass, and iron compounds may lead to the greenish cast oſten seen in less expensive commercial glasses. Selenium dioxide, while non-metallic, may be used in trace amounts to cancel out the iron-green color yielding a water-clear transparent glass without color cast. Higher amounts of selenium will produce a ruby-red glass distinctively different from the pink-red seen in gold-containing glasses. Te chemistry of colored glass is quite complex and is a constantly evolving area of study for manufacturers, with new colors appearing in the marketplace quite oſten. One technique commonly used in art glass is the creation
of a metallic “reduction” surface. Tese can be colorful, attractive surfaces and are popular in art glass jewelry. To produce this type of surface, a glass with a relatively high metal content is exposed to a flame with a high fuel-to- oxygen ratio (also known as a reduction flame). Tis flame chemistry tends to remove oxygen from metal oxides and leave the pure metal on the surface of the glass. Te color of this surface is oſten assumed to indicate the metal in question, and, combined with the names of stock glass colors, end users may reach erroneous conclusions about the actual chemical nature of the surface. Gold-appearing surfaces are oſten assumed to be gold, silver surfaces silver, etc. Analysis of these surfaces shows that apparent color and stock names may be misleading.
28
Materials and Methods Five samples of glass from two different manufacturers
were purchased on the open market. Tree glass samples from Effetre 456 Rubino Oro, one sample each of Effetre 264 Light Ivory, Effetre 236 Dark Turquoise, Effetre 271 Silver Plum (Effetre Glass, Murano, Italy), and one sample of Kugler 215 Gold Brown (Friedrich Farbglashütte GmbH, Kaufeuren- Neugablonz, Germany) were used in this study. Each glass type was supplied in 5-mm diameter rod form. Samples were prepared by making two small, round beads
(approximately 8–10 mm) of each glass in a neutral flame. One bead from each pair was kept as a control and the other was treated in such a way as to develop a metallic surface. Tree “lollipop” samples of Rubino were prepared by melting the ends of single rods from different batches, flattening the tips, and exposing them to a reducing flame to develop the color- reaction surface. Ivory glass is known to be reactive with metal colorants in other glass colors and was exposed to the torch plume from the Rubino glass. Te Silver Plum glass was exposed to a high oxygen flame to develop a metallic surface. All samples were examined in a LEO 1450 vp scanning
electron microscope operated at 20 kV, and images were collected in both secondary electron (SE) and backscatter electron (BSE) imaging modes. X-ray data were collected using a Rontec X-flash X-ray detector and microanalysis soſtware.
Results When exposed to a high-fuel flame, Rubino glass
darkened and developed a surface color ranging from silver to gold. Returning these samples to a hotter neutral flame caused the surface to lose the metallic sheen. It could be recreated by returning the glass to the reducing flame. Te three lollipop samples showed similar surface color development, even though the unheated rods had distinctly different levels of color and transparency. Control samples remained an intense transparent pink-red color (Figures 1A and 1B). Scanning electron microscopy (SEM) studies of the reduced surface showed small, bright islands of material in the BSE signal compared to the surrounding surface. Energy-dispersive X-ray microanalysis (EDS) of
doi:10.1017/S1551929510000891
www.microscopy-today.com • 2010 September
Figure 1: (A) Three color variants of Effetre 456 (Rubino Oro or Gold Pink) shown in rod form with reduced areas of silver and gold on the flattened tips. (B) The left bead shows the darkened metallic surface of the reduced glass whereas the right bead shows the pink-red color of the glass melted in a neutral flame.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76